The human heart wall consists of an inner layer of simple squamous epithelium, referred to as the endocardium, overlying a variably thick heart muscle or myocardium and is enveloped within a multi-layer tissue structure referred to as the pericardium. The innermost layer of the pericardium, referred to as the visceral pericardium or epicardium, clothes the myocardium. The epicardium reflects outward at the origin of the aortic arch to form an outer tissue layer, referred to as the parietal pericardium, which is spaced from and forms an enclosed sac extending around the visceral pericardium of the ventricles and atria. An outermost layer of the pericardium, referred to as the fibrous pericardium, attaches the parietal pericardium to the sternum, the great vessels and the diaphragm so that the heart is confined within the middle mediastinum. Normally, the visceral pericardium and parietal pericardium lie in close contact with each other and are separated only by a thin layer of a serous pericardial fluid that enables friction free movement of the heart within the sac. The space (really more of a potential space) between the visceral and parietal pericardia is referred to as the pericardial space. In common parlance, the visceral pericardium is usually referred to as the epicardium, and epicardium will be used hereafter. Similarly, the parietal pericardium is usually referred to as the pericardium, and pericardium will be used hereafter in reference to parietal pericardium.
It is frequently medically necessary to access the pericardial space to treat an injury, infection, disease or defect of the heart, e.g., an occluded coronary artery, a defective heart valve, aberrant electrical pathways causing tachyarrhythmias, and bacterial infections, or to provide cardiac resynchronization therapy, or to place epicardial pacing or cardioversion/defibrillation electrodes against the epicardium or into the myocardium at selected sites. It is necessary in these procedures to surgically expose and cut through the pericardium to obtain access to the pericardial space.
Highly invasive surgical techniques, referred to as a median sternotomy (open-chest surgical exposure) or a thoracotomy, have been typically employed to provide the surgeon access to the pericardial space and the heart. A median sternotomy incision begins just below the sternal notch and extends slightly below the xiphoid process. A sternal retractor is used to separate the sternal edges for optimal exposure of the heart. Hemostasis of the sternal edges is typically obtained using electrocautery with a ball-tip electrode and a thin layer of bone wax.
The open chest procedure involves making a 20 to 25 cm incision in the chest of the patient, severing the sternum and cutting and peeling back various layers of tissue in order to give access to the heart and arterial sources. As a result, these operations typically require large numbers of sutures or staples to close the incision and 5 to 10 wire twisted loops to keep the severed sternum together. Such surgery often carries additional complications such as instability of the sternum, post-operative bleeding, and mediastinal infection. The thoracic muscle and ribs are also severely traumatized, and the healing process results in an unattractive scar. Post-operatively, most patients endure significant pain and must forego work or strenuous activity for a long recovery period.
Many minimally invasive surgical techniques and devices have been introduced in order to reduce the risk of morbidity, expense, trauma, patient mortality, infection, and other complications associated with open-chest cardiac surgery. Less traumatic limited open chest techniques using an abdominal (subxiphoid) approach or, alternatively, a “Chamberlain” incision (an approximately 8 cm incision at the sternocostal junction), have been developed to lessen the operating area and the associated complications. In recent years, a growing number of surgeons have begun performing coronary artery bypass graft (CABG) procedures using minimally invasive direct coronary artery bypass grafting (MIDCAB) surgical techniques and devices. Using the MIDCAB method, the heart typically is accessed through a mini-thoracotomy (i.e., a 6 to 8 cm incision in the patient's chest) that avoids the sternal splitting incision of conventional cardiac surgery. A MIDCAB technique for performing a CABG procedure is described in U.S. Pat. No. 5,875,782, for example.
Other minimally invasive, percutaneous, coronary surgical procedures have been advanced that employ multiple small trans-thoracic incisions to and through the pericardium, instruments advanced through ports inserted in the incisions, and a thoracoscope to view the accessed cardiac site while the procedure is performed as shown, for example, in U.S. Pat. Nos. 6,332,468, 5,464,447, and 5,716,392. Surgical trocars having a diameter of about 3 mm to 15 mm are fitted into lumens of tubular trocar sleeves, cannulae or ports, and the assemblies are inserted into skin incisions. The trocar tip is advanced to puncture the abdomen or chest to reach the pericardium, and the trocar is then withdrawn leaving the sleeve or port in place. Surgical instruments and other devices such as fiber optic thoracoscopes can be inserted into the body cavity through the sleeve or port lumens. As stated in the '468 patent, instruments advanced through trocars can include electrosurgical tools, graspers, forceps, scalpels, electrocauteries, clip appliers, scissors, etc. The straight, stiff, cannular, instruments requires use of inherently difficult techniques including rotation of the heart and sometimes deflation of either lung in order to reach the posterior cardiac surfaces.
Therefore, much effort has been expended to develop medical devices and techniques to access the pericardial space employing minimally invasive percutaneous procedures. One difficulty has been that normally the pericardial space is so small or thin that it is difficult to penetrate the pericardium using miniaturized instruments capable of being introduced through a port to the site without also puncturing the underling epicardium and thereby, damaging the myocardium or a coronary vessel. Proliferative adhesions occur between the pericardium and the epicardium in diseased hearts and hamper access to the pericardial space employing such minimally invasive percutaneous procedures. The simple percutaneous approach can be used to penetrate the pericardium to drain a large pericardial effusion, i.e., an accumulation of too much fluid in the pericardial space that widens the pericardial space. A spinal needle (18–20 gauge) and stylet occluding the needle lumen are advanced incrementally in a superior/posterior fashion through a small (2–4 mm) cutaneous incision between the xiphoid and costal cartilage. Periodically, the stylet is removed, and fluid aspiration is attempted through the needle lumen. The advancement is halted when fluid is successfully aspirated, and the pericardial effusion is then relieved.
Methods and apparatus for accessing the pericardial space for the insertion of implantable defibrillation leads are disclosed in U.S. Pat. Nos. 5,071,428 and 6,156,009, wherein a forceps device is used to grip the pericardium and pull it outward to form a “tent”. In the '428 patent, a scissors or scalpel is introduced to cut the pericardium (pericardiotomy) under direct vision through a subxiphoid surgical incision. The forceps device disclosed in the '009 patent incorporates a mechanism for introducing electrical leads or guidewires through the outwardly displaced pericardium. Further methods and apparatus for accessing the pericardial space for the insertion of devices or drugs are disclosed in U.S. Pat. No. 6,423,051, wherein an access tube having a device access lumen is provided with a plurality of hooks in the tube distal end that can be used to hook into the pericardium to enable the lifting and “tenting” of the pericardium. A cutting instrument or sharpened tip guidewire or the like can be advanced through the device access lumen to perforate the pericardium.
Other methods and apparatus that are introduced through percutaneously placed ports or directly through small trans-thoracic incisions for accessing the pericardial space employ suction devices to grip the pericardium or epicardium as disclosed, for example, in U.S. Pat. Nos. 4,991,578, 5,336,252, 5,827,216, 5,868,770, 5,972,013, 6,080,175, 6,206,004, and 6,231,518 and the above-referenced '948 patent. The suction devices are configured like a catheter or tube having a single suction tool lumen and typically having a further instrument delivery lumen. The suction tool lumen terminates in a single suction tool lumen end opening through the device distal end in the '578, '252, '175, '770, and '013 patents and through the device sidewall in the '216 and '518 patents. Certain of these patents recite that the applied suction draws a “bleb,” i.e., a locally expanded region of the pericardium, into the suction tool lumen or a suction chamber at the device distal end. A needle can then be advanced into the bleb and used to draw off fluids or deliver drugs into the pericardial space, or the like. In addition, it is suggested in these patents that treatment devices including catheters, guidewires, and electrodes, e.g., defibrillation electrodes, can be advanced into the pericardial space through a device introduction lumen for a variety of reasons. Although theoretically plausible, the ability to reliably maintain a vacuum seal against the pericardium when such treatment devices are advanced can be problematic. Certain of these patents also disclose use of one or more expandable member or balloon introduced into the anatomic space, e.g., the pericardial space between the epicardium and the pericardium, wherein the expandable member is introduced into the anatomic space in a deflated state. The balloon or balloons are expanded in the pericardial space to dilate or retract the pericardial space to form a procedural field for the duration of the procedure, and then deflated to enable retraction from the pericardial space and the body.
Introduction and visualization catheters including endoscopes and device or fluid delivery catheters that incorporate one or more distal circumferential balloon in the manner of a Foley catheter that inflates around the circumference of the catheter distal end to lodge the catheter body distal end within an anatomic space or chamber of the heart or other body organ are well known in the art as exemplified by U.S. Pat. Nos. 4,040,413, 4,779,611, 5,250,025, and 6,099,498, for example. Circumferential balloon catheters that are introduced via a surgical incision through the pericardium into the pericardial space are disclosed in the above-referenced '252 patent and in U.S. Patent Application Publication U.S. 2003/0158464. The inflated circumferential balloon (or balloons) retain the distal end of the balloon catheter introduced through the pericardial incision within the pericardial space while a cardiac lead is introduced into the pericardial space and affixed to the epicardium.
Other balloon catheters that have a shaped bag or balloon or other expandable member at the distal end of the catheter body are disclosed in U.S. Pat. Nos. 5,402,772, 5,634,895, and 6,231,518, for example. Generally speaking, the bag or balloon or inflatable member is shaped to inflate to a greater expanded dimension in one direction extending laterally of the axis of the catheter body and to a lesser expanded dimension in the transverse direction extending laterally to the axis of the catheter body.
For example, a balloon catheter is disclosed in the above-referenced '518 patent that expands in the shape of a doughnut that is sandwiched between the pericardium and epicardium resulting in an open center that a drug or other material can be dispensed into to deliver the drug or material to a localized region of the epicardium.
A further drug delivery catheter adapted to be introduced into and inflated in the pericardial space is disclosed in the above-referenced '895 patent wherein a gaseous drug is pumped into a permeable balloon and is eluted through the wall of the permeable balloon applied against the epicardium and pericardium or wherein an iontophoretic delivery mechanism is employed to deliver drugs.
A number of inflatable retraction devices are disclosed in the above-referenced '772 for introduction into and expansion of various anatomic spaces. A set of tools and a complex procedure are employed to maintain the expansion while creating “windows” of the inflated retraction devices to pass other instruments through. The cage struts are inflated to enable selective expansion of the retraction device from a collapsed state into a polyhedral shape and deflated to enable contraction of the retraction device back into a collapsed state. Inelastic sheet panels extend between the cage struts, and other instruments are passed through windows formed through opposed sheets.
It would be desirable to provide additional and improved methods and apparatus that provide minimally invasive access to an anatomic space of a patient's body, particularly a patient's pericardial space to facilitate visualization of the pericardial space and introduction of devices or drugs or other materials and performance of medical and surgical procedures.